- ID:
- ivo://CDS.VizieR/J/MNRAS/469/4578
- Title:
- Deep learning classification in asteroseismology
- Short Name:
- J/MNRAS/469/4578
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the power spectra of oscillating red giants, there are visually distinct features defining stars ascending the red giant branch from those that have commenced helium core burning. We train a 1D convolutional neural network by supervised learning to automatically learn these visual features from images of folded oscillation spectra. By training and testing on Kepler red giants, we achieve an accuracy of up to 99 per cent in separating helium-burning red giants from those ascending the red giant branch. The convolutional neural network additionally shows capability in accurately predicting the evolutionary states of 5379 previously unclassified Kepler red giants, by which we now have greatly increased the number of classified stars.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/835/217
- Title:
- Density distributions for mm-wave line ratios
- Short Name:
- J/ApJ/835/217
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the use of mm-wave emission line ratios to trace molecular gas density when observations integrate over a wide range of volume densities within a single telescope beam. For observations targeting external galaxies, this case is unavoidable. Using a framework similar to that of Krumholz & Thompson (2007ApJ...669..289K), we model emission for a set of common extragalactic lines from lognormal and power law density distributions. We consider the median density of gas that produces emission and the ability to predict density variations from observed line ratios. We emphasize line ratio variations because these do not require us to know the absolute abundance of our tracers. Patterns of line ratio variations have the potential to illuminate the high-end shape of the density distribution, and to capture changes in the dense gas fraction and median volume density. Our results with and without a high-density power law tail differ appreciably; we highlight better knowledge of the probability density function (PDF) shape as an important area. We also show the implications of sub-beam density distributions for isotopologue studies targeting dense gas tracers. Differential excitation often implies a significant correction to the naive case. We provide tabulated versions of many of our results, which can be used to interpret changes in mm-wave line ratios in terms of adjustments to the underlying density distributions.
- ID:
- ivo://CDS.VizieR/J/AJ/81/807
- Title:
- Deprojection of the r^1/4^ law tables
- Short Name:
- J/AJ/81/807
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A spherical galaxy with reduced surface brightness, J=B({alpha})/B_e_, obeying the r^1/4^ law, logJ=-3.3307 ({alpha}^1/4^-1), where {alpha} is the reduced radius, {alpha}=r/r_e_ (r_e_ is the effective radius), is deprojected to find the corresponding space density, mass, mean density, force, potential, escape velocity, and potential energy at each point in the galaxy. Numerical tabulations to five significant figures are given for 124 points in the range 10^-6^<=R/r_e_<=260. In addition the projected surface brightness B({alpha}) and integrated luminosity within {alpha} are tabulated for the range 10^-6^<={alpha}=r/r_e_<=260. Conversion factors to cgs units and to M_{sun}_, pc, km/s, L_{sun}_ units are given. Asymptotic expansions for the space density {rho}(s) in the ranges s=<10^-4^ and s>=10^-1^ are derived, and it is demonstrated that the projection of the expansion for s<=10^-1^ is almost indistinguishable from the r^1/4^ law itself, apart from a small excess of luminosity in the central regions. Formulae and numerical tables of the luminosity distribution are given for use in galaxy photometry. Relations between the total galactic mass M_T_, the effective radius r_e_, the velocity dispersion {sigma}_v_, the central density {rho}_c_ and the mass M_N_ and radius R_N_ of the nucleus are derived. Here the "nucleus" is defined as the region within which stars having a velocity equal to the mean velocity dispersion in space, {sigma}_v_.
- ID:
- ivo://CDS.VizieR/J/ApJ/699/453
- Title:
- Determination of black hole masses
- Short Name:
- J/ApJ/699/453
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of correlations between X-ray spectral and timing properties observed from a number of Galactic black hole (BH) binaries during hard-soft state spectral evolution. We analyze 17 transition episodes from eight BH sources observed with Rossi X-Ray Timing Explorer. Our scaling technique for BH mass determination uses a correlation between the spectral index and quasi-periodic oscillation (QPO) frequency. In addition, we use a correlation between the index and the normalization of the disk "seed" component to cross-check the BH mass determination and estimate the distance to the source. We use GRO J1655-40 as a primary reference source for which the BH mass, distance, and inclination angle are evaluated by dynamical measurements with unprecedented precision among other Galactic BH sources. We apply our scaling technique to determine BH masses and distances for Cygnus X-1, GX 339-4, 4U 1543-47, XTE J1550-564, XTE J1650-500, H 1743-322, and XTE J1859-226. A good agreement of our results for sources with known values of BH masses and distance provides independent verification for our scaling technique.
- ID:
- ivo://CDS.VizieR/J/ApJ/771/L45
- Title:
- 3D global climate models for exoplanet around M-star
- Short Name:
- J/ApJ/771/L45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The habitable zone (HZ) is the circumstellar region where a planet can sustain surface liquid water. Searching for terrestrial planets in the HZ of nearby stars is the stated goal of ongoing and planned extrasolar planet surveys. Previous estimates of the inner edge of the HZ were based on one-dimensional radiative-convective models. The most serious limitation of these models is the inability to predict cloud behavior. Here we use global climate models with sophisticated cloud schemes to show that due to a stabilizing cloud feedback, tidally locked planets can be habitable at twice the stellar flux found by previous studies. This dramatically expands the HZ and roughly doubles the frequency of habitable planets orbiting red dwarf stars. At high stellar flux, strong convection produces thick water clouds near the substellar location that greatly increase the planetary albedo and reduce surface temperatures. Higher insolation produces stronger substellar convection and therefore higher albedo, making this phenomenon a stabilizing climate feedback. Substellar clouds also effectively block outgoing radiation from the surface, reducing or even completely reversing the thermal emission contrast between dayside and nightside. The presence of substellar water clouds and the resulting clement surface conditions will therefore be detectable with the James Webb Space Telescope.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A96
- Title:
- Disk-locking PMS evolutionary tracks
- Short Name:
- J/A+A/586/A96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotational evolution in young stars is described by pre-main sequence evolutionary tracks including non-gray boundary conditions, rotation, conservation of angular momentum, and simulations of disk-locking. By assuming that disk-locking is the regulation mechanism for the stellar angular velocity during the early stages of pre-main sequence evolution, we use our rotating models and observational data to constrain disk lifetimes (Tdisk) of a representative sample of low-mass stars in two young clusters, the Orion Nebula cluster (ONC) and NGC 2264, and to better understand their rotational evolution. The period distributions of the ONC and NGC 2264 are known to be bimodal and to depend on the stellar mass. To follow the rotational evolution of these two clusters' stars, we generated sets of evolutionary tracks from a fully convective configuration with low central temperatures (before D- and Li-burning). We assumed that the evolution of fast rotators can be represented by models considering conservation of angular momentum during all stages and of moderate rotators by models considering conservation of angular velocity during the first stages of evolution. With these models we estimate a mass and an age for all stars.
- ID:
- ivo://CDS.VizieR/J/AJ/155/165
- Title:
- Dissipation in exoplanet hosts from tidal spin-up
- Short Name:
- J/AJ/155/165
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stars with hot Jupiters (HJs) tend to rotate faster than other stars of the same age and mass. This trend has been attributed to tidal interactions between the star and planet. A constraint on the dissipation parameter Q_*_' follows from the assumption that tides have managed to spin up the star to the observed rate within the age of the system. This technique was applied previously to HATS-18 and WASP-19. Here, we analyze the sample of all 188 known HJs with an orbital period <3.5 days and a "cool" host star (T_eff_<6100 K). We find evidence that the tidal dissipation parameter (Q_*_') increases sharply with forcing frequency, from 10^5^ at 0.5 day^-1^ to 10^7^ at 2 day^-1^. This helps to resolve a number of apparent discrepancies between studies of tidal dissipation in binary stars, HJs, and warm Jupiters. It may also allow for a HJ to damp the obliquity of its host star prior to being destroyed by tidal decay.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/50
- Title:
- Distance to Cepheids using the Wesenheit function
- Short Name:
- J/ApJ/747/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we explore the possibility of using the Wesenheit function to derive individual distances to Galactic Cepheids, as the dispersion of the reddening-free Wesenheit function is smaller than the optical period-luminosity (P-L) relation. When compared to the distances from various methods, the averaged differences between our results and published distances range from -0.061 to 0.009, suggesting that the Wesenheit function can be used to derive individual Cepheid distances. We have also constructed Galactic P-L relations and selected Wesenheit functions based on the derived distances. A by-product from this work is the derivation of Large Magellanic Cloud distance modulus when calibrating the Wesenheit function. It is found to be 18.531+/-0.043 mag.
- ID:
- ivo://CDS.VizieR/J/A+A/559/A85
- Title:
- 1D Lya forest power spectrum
- Short Name:
- J/A+A/559/A85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed two independent methods to measure the one-dimensional power spectrum of the transmitted flux in the Lyman-{alpha} forest. The first method is based on a Fourier transform, and the second on a maximum likelihood estimator. The two methods are independent and have different systematic uncertainties. The determination of the noise level in the data spectra was subject to a novel treatment, because of its significant impact on the derived power spectrum. We applied the two methods to 13,821 quasar spectra from SDSS-III/BOSS DR9 (Baryon Oscillation Spectroscopic Survey, BOSS, 2013AJ....145...10D) selected from a larger sample of over 60,000 spectra on the basis of their high quality, large signal-to-noise ratio, and good spectral resolution. The power spectra measured using either approach are in good agreement over all twelve redshift bins from <z>=2.2 to <z>=4.4, and scales from 0.001(km/s)^-1^ to 0.02(km/s)^-1^. We determine the methodological and instrumental systematic uncertainties of our measurements.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A101
- Title:
- 3D MHD models angular quadratures
- Short Name:
- J/A+A/645/A101
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Accurate angular quadratures are crucial for the numerical solution of three-dimensional (3D) radiative transfer problems, especially when including the spectral line polarisation produced by the scattering of anisotropic radiation. There are two requirements for an optimal quadrature that are difficult to satisfy simultaneously: high accuracy and short computing time. Recently, imposing certain symmetries, we have derived a set of near optimal angular quadratures. Here we extend our previous investigation by considering other symmetries. Moreover, we test the performance of our new quadratures by numerically solving a radiative transfer problem of resonance line polarisation in a 3D model of the solar atmosphere resulting from a magneto-hydrodynamical simulation. The new angular quadratures derived here outperform the previous ones in terms of the number of rays needed to achieve any given accuracy.
